Treadmill Electrical Problem

I have a treadmill that is about 9 years old, but saw very limited use so there is very little wear and tear.

Before I get into the electrical details, here's the problem and what leads me to believe it's electrical.

I noticed that the treadmill is not getting up to full speed. When I follow the instructions and enter calibration mode and select the fastest speed (10 mph) it only gets up to about 8 mph. I have the potentiometer set to the fastest setting and it still will not spin above 8 mph.

None of the LED's on the control boards indicate a problem anywhere.

One thing I notice is the sound of sparking in the motor, and I can see some flickering going on where the black wire/brush is in the motor.

When I have the treadmill running at 8 mph, when I get on it it sounds like the motor is struggling and the sparking noise increases, almost as if it's trying to keep up with me.

I tested the voltage coming out of the control board and got the following voltage readings for each speed setting:

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Sparking in a DC motor is normal to some degree. This is the brushes on the commutator. Increasing noise due to higher mechanical load on the motor is also not unusual. The motor is DC not AC. The treadmill is powered by 120V AC.

You might have a problem with the drive electronics for the DC motor but this simply could be a limitation of the design.

You have your bases covered....but let me ask you this, how do you know it's not achieving 10 mph...by the machines own readout? Or do you just sense it when running on it. The difference between 5 and 10 is quite noticable....but 8 to 9.....is that perceiveable when running?

Yes, I can tell the difference because even when increasing the speed slowly through the different speeds, you can hear the motor increase. That, and I know something is wrong because when I start running on it, the motor sounds like it's struggling to keep up and it slows down. I just have this feeling that the control board isn't sending enough voltage for the motor to get up to speed, as well as allow the motor to keep up under load.

Whats the brand and model number? most treadmills have board calibrations that you can do from the user controls.

It sounds like a calibration or board issue. There should be a magnetic reed switch which counts the RPM of either the motor or the front drum. Make sure it's pointed towards the magnet properly.

You have a DC motor. The board detects the pulses from the reed switch and calculates the RPM from that. If the pulses are lower, it will increase the voltage to the motor to speed everything up. If the motor is spinning too fast, it will cut the voltage (DC) to slow the motor down.

How is the condition of the deck and belt? The deck and belt need periodic cleaning and lubricating. The deck has a special surface, and if not taken care of properly, will wear out quickly. This will cause a large amount of friction between the deck and belt surface.

The manufacturer said it sounded like a problem with the Speed Control Module so they sent me out a new one. He provided a return slip and said as long as I test it without mounting it, if it isn't the problem I can return it. I figured I might as well spend $100 on a part and wish for the best than spend money having someone to come out here and tell me I need the part anyway.

This thing was barely used and just sat around for the past 4 or 5 years so I'm shocked that part could go bad but I guess anything can happen.

There is a drive (control board) that controls motor speed. Is it DC or AC voltage you are reading? KB makes many of the drives for these treadmills and are very easy to troubleshoot. Since you say its a DC motor we will accept that as fact.
The control board takes AC power and converts it to DC. Standard DC motors in this HP range are usually either 90 VDC or 180 VDC.
Your motor sounds like it is a 90 VDC motor. Check the motor nameplate and verify voltage and current. As your input voltage is 120 VAC.
At zero speed (stop) you should read little to no voltage going to the motor. At full speed you should read 90 volts. At half speed you should read approximately 45 volts. See the Volts per RPM example? Understand?
Now. Here is how you tune this control.

1) Attach/clip meter leads to output conductors (wires) going to the motor.
2) Speed the machine to full. Take meter reading. It should be near 90 volts. (Yours is not)
3) Reduce speed to zero. (stop) Take meter reading. Should read zero or very close.
4) Now turn the "min" pot (CW) on the board until the motor just barely tries to turn. (this is a potentiometer located on the board for minimum speed). Turn it (CCW) until it just stops. You want it wanting to turn but not turning.
5) Now, return the machine to full speed and check the voltage. Turn the "max" (maximum) speed pot on the control board to achieve 90 volts. (CW or CCW)
6) Continue back and forth at full speed and zero speed until the control board is out putting the correct voltage for the speed. Each time you turn either pot, it effects the other pot.

These steps are intended for a DC controller and a 90 volt PM, DC motor. Should the controller (DC Drive) output these voltages correctly, then you must check your motor. A good cleaning of the motor may be in order.
Use extreme caution dissembling a DC motor. There are many parts and it will be very difficult to reassemble.
Let us know how the tuning procedure works out. Good luck and take your time.

Checking the current can be completed with the use of your multimeter. Consult your meter instructions in regard to (amps/current) measurements. This is a bit more dangerous as you will need to put your meter in series with the motor. Checking the current may not be required, but may help determining the issue, if the tuning procedure does not correct your problem.

Does this mean at full speed, the motor should be getting 95 volts? It doesn't appear to be coming even close to that, which to me indicates a control board problem?[/quote]

Measuring voltage is not really an accurate way of measuring drive to the motor, as the output from the controller might not be strictly sinusoidail !

Some sparking in motors is nomal,
But excessive sparking could indicate a dirty commutator.
which could explain reduced output.
Can you take apart the motor and clean the comutator ?
Very fine sand paper is used.